1. Field of the Invention
The invention relates to a new type of low temperature bleaching system and a method of cleaning substrates therewith.
2. The Related Art
Many household and personal care products are formulated with an active oxygen-releasing material to effect removal of stain and soil. Oxygen-releasing materials have an important limitation; their activity is extremely temperature dependent. Temperatures in excess of 60.degree. C. are normally required to achieve any bleach effectiveness in an aqueous wash system. Especially for cleaning fabrics, high temperature operation is both economically and practically disadvantageous.
The art has partially solved the aforementioned problem through the use of activators. These activators, also known as bleach precursors, often appear in the form of carboxylic acid esters. In an aqueous liquor, anions of hydrogen peroxide react with the ester to generate the corresponding peroxyacid which oxidizes the stained substrate. Commercial application of this technology is found in certain fabric bleaching detergent powders incorporating tetraacetylethylenediamine (TAED) and sodium nonanoyloxybenzene sulfonate (SNOBS).
TAED is effective only under warm-hot wash conditions, i.e. above 30.degree. C. Although this material is widely employed in Europe with laundry detergent, cold water consumer washing habits have not permitted use in the United States. SNOBS can operate at lower temperatures than TAED. For this reason, it has been commercialized in the United States but its performance could still be improved.
Another problem with carboxylic acid ester precursors such as TAED and SNOBS is that conversion to peracid is inefficient. A further difficulty is that they are not catalytic. Once the ester has been perhydrolyzed, it can no longer be recycled. Accordingly, relatively large amounts of precursor are necessary. Amounts as high as 8% may be necessary in a detergent formulation for bleaching fabrics. At such high use levels, cost for these relatively expensive chemicals is of major concern.
Recently there has been reported in U.S. Pat. No. 5,047,163, U.S. Pat. No. 5,045,233 and U.S. Pat. No. 5,041,232, all to Batal and Madison, a system for activating bleach precursors based upon sulfonimines and N-sulfonyloxaziridines. While these compounds have been shown to be highly effective, even better catalysts are sought, especially for wash temperatures around 10.degree. C., such as are experienced in Japan.
Outside the context of consumer products, there have been reports of catalytic oxidizing agents. Hanquet and coworkers, in a series of articles, reported preparation of a new class of stable olefin epoxidizing agents, namely oxaziridinium salts. See Hanquet, Lusinchi and Milliet, Tet, Let. (1988) 3941; Hanquet, Lusinchi and Milliet, C. R. Acad. Sci. Paris (1991) Series II, 625; and Hanquet, Lusinchi and Milliet, Tet. Let. (1988) 2817. These oxaziridinium salts were prepared by peracid or monopersulfate oxidation of a corresponding quaternary imine salt under alkaline conditions. Epoxides were reported to be formed from the reaction of olefins with the oxaziridinium salts. Reactions were conducted either in organic solvents or in organic solvent-water biphasic media. Beyond use as a synthetic tool, there is no suggestion of any possible application for quaternary imine salt chemistry to the problem of removing stains in consumer applications, such as in cleaning fabrics.
It is an object of the present invention to provide an improved bleaching system and detergent composition containing such system that operates over a wide temperature range including that of under 30.degree. C.
It is another object of the present invention to improve the performance of bleach precursors that normally would be inoperative under low temperature wash conditions.
A further object of the present invention is to provide bleach improvement through catalysts effective in relatively small amounts so as to avoid any substantial incremental costs.
A still further object of the present invention is to provide a method for bleaching stained substrates such as clothes, household hard surfaces including sinks, toilets and the like, and even dentures.
Other objects of the present invention will become more readily apparent through the following summary, detailed description and examples.